Defined in header <type_traits> | ||
---|---|---|
template< class T > struct is_function; | (since C++11) |
Checks whether T
is a function type. Types like std::function
, lambdas, classes with overloaded operator()
and pointers to functions don't count as function types. Provides the member constant value
which is equal to true
, if T
is a function type. Otherwise, value
is equal to false
.
T | - | a type to check |
template< class T > inline constexpr bool is_function_v = is_function<T>::value; | (since C++17) |
value
[static] | true if T is a function type , false otherwise (public static member constant) |
operator bool | converts the object to bool , returns value (public member function) |
operator()
(C++14) | returns value (public member function) |
Type | Definition |
---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
// primary template template<class> struct is_function : std::false_type { }; // specialization for regular functions template<class Ret, class... Args> struct is_function<Ret(Args...)> : std::true_type {}; // specialization for variadic functions such as std::printf template<class Ret, class... Args> struct is_function<Ret(Args......)> : std::true_type {}; // specialization for function types that have cv-qualifiers template<class Ret, class... Args> struct is_function<Ret(Args...) const> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) volatile> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const volatile> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) volatile> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const volatile> : std::true_type {}; // specialization for function types that have ref-qualifiers template<class Ret, class... Args> struct is_function<Ret(Args...) &> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const &> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) volatile &> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const volatile &> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) &> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const &> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) volatile &> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const volatile &> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) &&> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const &&> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) volatile &&> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const volatile &&> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) &&> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const &&> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) volatile &&> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const volatile &&> : std::true_type {}; // specializations for noexcept versions of all the above (C++17 and later) template<class Ret, class... Args> struct is_function<Ret(Args...) noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) volatile noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const volatile noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) volatile noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const volatile noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) & noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const & noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) volatile & noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const volatile & noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) & noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const & noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) volatile & noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const volatile & noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) && noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const && noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) volatile && noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args...) const volatile && noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) && noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const && noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) volatile && noexcept> : std::true_type {}; template<class Ret, class... Args> struct is_function<Ret(Args......) const volatile && noexcept> : std::true_type {}; |
#include <iostream> #include <type_traits> struct A { int fun() const&; }; template<typename> struct PM_traits {}; template<class T, class U> struct PM_traits<U T::*> { using member_type = U; }; int f(); int main() { std::cout << std::boolalpha; std::cout << std::is_function<A>::value << '\n'; std::cout << std::is_function<int(int)>::value << '\n'; std::cout << std::is_function<decltype(f)>::value << '\n'; std::cout << std::is_function<int>::value << '\n'; using T = PM_traits<decltype(&A::fun)>::member_type; // T is int() const& std::cout << std::is_function<T>::value << '\n'; }
Output:
false true true false true
(C++17) | checks if a type can be invoked (as if by std::invoke ) with the given argument types (class template) |
(C++11) | checks if a type is an object type (class template) |
(C++11) | checks if a type is a non-union class type (class template) |
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